Field
The present invention relates generally to card (e.g. NFC or RFID) protection. More specifically, present invention relates to methods and devices for protecting cards, such as NFC or RFID cards, from harmful magnetic fields.
Background
Approaches are being developed that use over the air power transmission between a transmitter and the device to be charged. These generally fall into two categories. One is based on the coupling of plane wave radiation (also called far-field radiation) between a transmit antenna and receive antenna on the device to be charged which collects the radiated power and rectifies it for charging the battery. Antennas are generally of resonant length in order to improve the coupling efficiency. This approach suffers from the fact that the power coupling falls off quickly with distance between the antennas. So charging over reasonable distances (e.g., >1-2 m) becomes difficult. Additionally, since the system radiates plane waves, unintentional radiation can interfere with other systems if not properly controlled through filtering.
Other approaches are based on inductive coupling between a transmit antenna embedded, for example, in a “charging” mat or surface and a receive antenna plus rectifying circuit embedded in the host device to be charged. This approach has the disadvantage that the spacing between transmit and receive antennas must be very close (e.g. mms). Though this approach does have the capability to simultaneously charge multiple devices in the same area, this area is typically small, hence the user must locate the devices to a specific area.
A device, such as a Near Field Communication (NFC) or RFID card, may receive excessive power from a wireless power transmitter when located within a charging area of the wireless power transmitter, even if the card operates on a different frequency than that used by a wireless power transmitter. Receiving excessive power may result in loss of power to the intended devices and possibly damage the card due to overheating. A need exist for methods, systems, and devices for protecting a device from excessive power generated by a wireless power transmitter.